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Full text of "Modern Mechanical Engineering Vol-I"

THE  ESSENTIALS  OF  ECONOMICAL  MACHINING    203

pieces, it is not permissible to clamp directly on their upper surfaces.
Lateral pressure is adopted in such cases, and also for those where the
upper surfaces have to be machined all over. The clamps are better if set
diagonally (fig. 35) to exer-
cise a downward pressure.
Often it is necessary to
set a stop against one end
of the work in the line of
direction of the cutting-tool
in order to prevent the occur-
rence of slip by reason of
the pressure in the longi-
tudinal direction. For hold-
ing substantial pieces, direct
clamping is adopted. But,
since tall bolts are apt to be
unstable under the stress of
heavy cutting, advantage is
taken of the presence of
suitable lower sections on
which to bed the clamps.
These may be stout flanges,
bosses, bores, or recessed portions, to be utilized by the judgment of the
machinist.

Cylindrical and Bored Work.—This is located and held in vee
blocks, which ensure parallelism of the work with the table.   Parallel shafts

Work

Fig. 36.—Large Vee Block and Vee'd Clamp

Sectional Elev
Fig. 37.-—Vee Blocks for Two Shafts, Clamp Plates adjusted with Grub-screws and thrown off with Springs

S,   Throw-offSprings
Gt Grub Screws for Adjust-
ment of Clamfs

and tubular portions of castings when located in vees of equal heights will
lie parallel with the table. If shafts are put through holes, and laid in
vees, the holes will be parallel. The clamps are variously set, according
to outlines, dimensions, and the avoidance of portions to be machined.